1. Field of Invention
This invention relates to porous ball bearing cages and more particularly to providing an improved lubricant reservoir within a ball bearing cage.
2. Description of the Prior Art
In porous ball bearing cages it is desirable that after impregnating the cage with an initial supply of lubricant that the lubricant be made available in a uniformly controlled manner to provide the critical elastohydrodynamic film between the balls and the raceways over the lifetime of the bearing. Presently, the desirable characteristics are not available to the satisfactory degree in porous ball bearing cages made of existing materials.
In the past, many attempts have been made to fabricate cages of porous materials such as sintered porous metals, or sintered porous polyimides as disclosed in U.S. Pat. No. 3,027,626 issued to J. J. Murphy, for the purpose of providing a reservoir of lubricant within the cage. However, all of these attempts have had shortcomings such as limited lubricant reservoir capacity, loss of lubricant at high centrifugal cage speeds, uneven distribution of lubricant between the retainer raceway and the bearing member, leakage of lubricant along the retainer side walls. The foregoing shortcomings can be attributed to low porosity; nonuniform distribution of pores; variations in pore size; and the orientation of pores and openings. The low porosity; i.e., less than five percent of the volume, results in insufficient lubricant storage capacity with a subsequent reduction in bearing life span. The nonuniform distribution of pores effects the strength and speed sensitivity of the bearing along with nonuniform feeding of lubricant to the bearing raceways. Ther orientation of some of the pores has resulted in the oil bleeding out radially due to centrifugal force rather than tangentially toward the balls. Additionally, secondary machining operations on these materials after sintering, result in uncontrolled closure and/or enlargement of the pores at the desired contact surfaces between the balls and the raceways. The uncontrolled closure of the pores may prevent oil from moving from the reservoir in the cage to the ball contact surface thus rendering the stored lubricating oil unusable. Obversely, enlargement of the pores may at noncontacting surface areas cause unwanted seepage of lubricant from the reservoir resulting in a shortened reservoir life span.